1. Field of the Invention
The present invention relates to photoelectric conversion apparatus, and more particularly to apparatus suitable for use in a facsimile device, an image reader, a digital copying device or the like which reads image information from an original by moving the document relative to such a device in contact therewith.
2. Related Background Art
Most conventional photoelectric conversion apparatuses of this (called a contact type photoelectric conversion apparatus) use an array of rod lenses or focusing fibers to project an image on a document to a photosensor or a group of photosensors including a photoelectric conversion element to thereby read the image.
For cost reduction and miniaturization purposes, photoelectric conversion apparatus have recently been developed extensively which include a thin transparent protective layer formed on a photosensor whereby a document is moved in contact with the protective layer to read the document.
FIG. 1 is a schematic of a cross sectional view showing one part of a photoelectric conversion apparatus of this type.
FIG. 2 is an equivalent circuit diagram of one part of the conversion apparatus.
As shown in FIG. 1, the light emitted from a light source (not shown) disposed on the back side of a transparent insulating substrate 1 is irradiated onto a document 7 through an opening 11 provided on the opposite side of the substrate 1 and the light reflected by the document is now irradiated onto a photoelectric conversion section 12 through a light entrance opening 11. The irradiated quantity of light according to the image information of the original 7 changes the conductivity of a semiconductor layer correspondingly, the electric charges produced by photoelectric conversion at the photoelectric conversion section 12 (corresponding to Rs in FIG. 2) are stored in an upper layer electrode 6 of an electric charge storage section 13 (corresponding to Cs in FIG. 2).
The photoelectric conversion section 12 and the electric charge storage section 13 include an opaque layer 2 and a lower layer electrode 3, respectively, formed on a common transparent insulating substrate 1. The sections 12 and 13 further include an insulating layer 4, a semiconductor layer 5 and an upper opaque layer electrode 6 in this order on the layers 2 and 3 with the light entrance opening 11 in the upper layer electrode 6 which constitutes part of the photoelectric conversion section 12. The sections further include in common a plurality of transparent insulating protective layers 301, 302, 303 on the upper layer electrode 6.
However, since the uppermost transparent insulating protective layer 303 has a generally high insulation in the conventional apparatus, static charges are produced on the protective layer 303 as the document 7 moves along the protective layer 303 while contacting same. A stray capacitance Cp formed as shown in FIG. 2 may cause level shifting of a signal or a malfunction of a signal processor.